Outline

Objective: The objective of this study was to investigate the reliability of MRI- and 3-dimensional, computer-guided targeting of the subthalamic nucleus (STN) by comparing the planned target with the final position of the electrode after microelectrode recording (MER) and intraoperative macrostimulation. In addition, the differences in defining the outer margins of the STN between 3D-MRI visualization and multi-trajectory microelectrode recording were investigated.

Methods: 26 STN targets in 13 patients with Parkinson's disease were investigated. The stereotactic coordinates of the antero-dorso-lateral subthalamic nucleus (STN) were determined directly, on axial and coronal T2WI spin echo slices after fusion of data sets. Intraoperatively, 3-5 parallel microelectrodes were inserted with the centre trajectory along the MRI-planned route. The final target point, as well as the outer margins of the STN according to MER and intraoperative clinical testing were superimposed on the preoperative MRI on a computer based, stereotactic planning workstation.

Results: In the cranio-caudal direction (z-coordinate) the differences between MRI derived targets and the final targets were most prominent (p<0,005). The final targets were found more superior with a mean of 1.5mm (range from 4.1 mm to -2.0 mm) and more anterior (mean: 1.0 mm; range: 3.4 mm to -2.7 mm; p<0,005) than the MRI derived targets. The differences concerning the laterality were not statistically significant, however, differences between +1.7 mm and -1.7 mm occurred. In 13 cases we recorded STN signals superior to the dorsal margins of the STN as detected on the 3D MRI (mean: 1.6 mm; standard deviation: 1.4 mm). In 2 cases we found STN signals more inferior MRI (mean: 1.4 mm), in 7 cases more lateral (mean: 1.1 mm; standard deviation: 1.1 mm) and in 1 case more posterior.

Conclusions: Microelectrode recording and intraoperative clinical testing lead to different target points than MRI directed and computer assisted, preoperative targeting. Furthermore, the functional STN in this study is not identical with the anatomical STN on MR images.